Paper manufacture



April l5, 1932. c. s. HAMM PAPER MANUFACTURE- 2 Sheets-Sheet Filed April1o'. 195o April 5, 1932; c. s. HAMM PAPER MANUFACTURE Film1 April 10,195o 2 Sheets-Sheet dftofnwq 5 CHARLES s. HAMM, or DAYTON, OHIO,

TION,-OF WILMINGTON, DELAWAN Patented Apr. 5, 1932 UNITED STATES PATENT;OFFICE AssIGNon 'ro MEAD PArERBOAnD oo'nroaAl E, A CORPORATION orDELAWARE PAPER MANUFAOTUBE Application filed April 10,

lThis: invention relates 4to the manufacture l ofthe pulp product isobtained, while insuring ease of handling of the material and theformation of paper therefrom at desired high Speeds.

Another object o'f this invention is to prof' y carrying transverse videa method of cooking fibrous materials o this character, in'which desiredcontrol of the cooking treatment'is effected by proportion# ing of thechemicals used in the cook to give a product of desired quality anduniformity.

Another object of the invention is to pro- -vide a method of extractingtannic acid from deciduous wood, such as chestnut chips, and thenpulping the extracted or leached wood, in which the leaching treatmentis coordinated with the subsequent pulping treatmentv to give an extractof desired purity and a pulp product of controlled quality.

Still anotherobject of this invention is to provide apparatus forcarrying out the above method, which apparatus is simple inconstruction. and highly effective and readily controlled in operation.ix v 'Other objects and advantages of the invention will be apparent frdmthe following description, the accompanying drawings and' ythe appendedclaims. Y In the drawings, in which like characters of referencedesignate like partsthroughout the L, several views thereof- Fig. 1 is adiagrammatic side elevational view of a portion of the apparatus forcarry ing out the method of this invention;

' Fig. 2 is a diagrammatic side elevational view of the remainingportion ofthe apparatus. Fig. 1 showing that portion of the apparatus tothe left of the line A--A and Fig. 2 that part to the right of suchline; and

Fig. 3 is a diagrammatic side elevational view' at right angles tOFig.Lof a portion of the apparatus. l

trough`21 within which travels 193i). Serial N0. 443,213.

Referring to the drawings, in which a pref erred embodiment of apparatusfor carrying out the method of this invention is disclosed, a chipperfor reducing pieces of wood or logs to chips is indicated at 10.Thischipper may be of conventional construction, and isv provided with afeeding inlet 11 through which the logs are introduced and a dischargeoutlet 12 through which the chips subdivided to a suitable size aredischarged onto a traveling conveyor 13. The conveyor 13 may be of anysuitable type, such asthat having a trough 14, on the surface of chain15 supported by rolls 16 and 17 and drags 18, which serve to drag thechips up the troughin the direction of the arrow and discharge them ontoa second `traveling' conveyor 20.

The'conveyor 2O is constructed similarly the conveyor 13 in that it isprovided with a the endless chain or belt 22 supported by rolls 23 and24 and carrying transverse drags. 25. The trough 21 is provided with,spaced openings 26 adapted to be controlled by suitable slide valves 27,throughwhich the material moved along the trough 21 may` fall intolinclined chutes 28. Each of the chutes 28 is inclined ,downwardly andalso laterally so as to clear which travels an endless l soI belt.Thelower ends ofthe chutes 28 dis- A charge las vindicated y leachingtanks 30,6in'which the leaching of the chips for the extraction of tanmcacid is accomplished. The arrangement shown 1s,

known as an open tank leach,'in which the at 29 into a plurality of'tubs are Open to atmosphere and the' While steam pipes 34. Preferably,when a number tion of extracted tannic acid, is passed into 1li-contactAwith the chips in a leaching tank sequence or in alternation; asoneleachingtub ofleaching vessels are used in series, the leachingliquid is passedthrough the vessels in a counter-current flow. That is,the most concentrated leaching liquor, or Water soluwhich has just beenconnected in the series,

' so that the concentrated liquor will be brought into contact withfreshchips; While the tank which has been connected in the series for thelongest time is treated with fresh Water so that an eective extractionis obtained.

The leaching tubs may thus be-operated in which has been in leachingoperation for `the longest time is cutout, a new leaching tub with freshchips is brought into operation, permitting the leached chips inthe tubwhich has been cut out to be removed. This tub is then refilled withfresh chips, and is ready to be again cut in at the other end of theleach liquor line, that is at the fresh `Water end. The Water introducedintothe first-tub of the series, as by the ipe 33, percolates throughthe chips Within the leaching tub and discharges through valvecontrolled pipe 35. Each valve controlled pipe communicates withsuitable conventional piping (not leaching tanks which are lconnected 1nseries'. -For example, ten tanks may be run; in series shown) by whichthe liquor discharging from a first tubinay be passed to the second tubof the series, and so on through the group of with counter-flowcirculation. The concentrated leach liquor from the last tub of theseries is'discharged into a-lefach liquor outlet pipe 36, whichcommunicates With all the Vtubs and leads to a storage tank (not's'hown)from which the leach liquor may besufpplied tothe evaporators andconcentratedto produce thei tannic extract of commerce.- When a leachingtub is cutlout'ofthe leachv ing operatlon, the extracted lchips thereinare then permitted to drain for a time are removed at through theperforate 32, the drained liquor being removed through pipes 35 and 36,vand` then the drained chips tub. `As shown, each leaching tub isprovlded with a leach caster, which comprises a central vertical shaft40 supported in suit-- able bearings and driven throughgears 41 and 42from ashaft 43, which is adapted to be connected to a suitable source ofpower by a clutch (not shown), so that the shaft grid or lattice Work acontrolled rate from the 43 and leach caster may be brought into-opshaft 40 for vertical movement thereon and is keyed thereto so as torotate with shaft 40. The stirring arm 44 carries a `plurality ofdepending inclined blades or ngers 45 which are so inclinedas tomove.the chips toward the periphery of the tank iipon rota- 'l tion of theshaft 40 and arm 44. The construction is-suchthat the arm 44 rests onthe surface of the chipsvwithin the leaching tub and slides verticallydown 'the shaft 40 as the level of the' chips .falls .due to discharge lof the chips from the tub, the arm thus rotating with the shaft 40 Whileresting on the surface of the chips. Adjacent the periphery of each tank30, a port or opening 47 is provided in the perforate grid 32, which isadapted to vbe opened f or closed by a sliding plate valve 48. The

opening 47 is in alignment with a discharge pipe49 extending from thebottom ofthe tank, and adapted to discharge onto atraveling conveyor 50..Each discharge pipe 49 is also controlled-*by a sliding plate valve 51.

`When the draining operation in the leaching.l

tank is completed, the valve 35 is closed and the va1ves`48 and 51opened. The leach caster is then started, serving to move the vchips tothe periphery of the tank and out through the discharge pipe 49. Therate at which the chips are fed to the periphery of the tank anddischarged is-controlled by the rate of rotation of the shaft 40, whichmay be controlled from-the line shaft in any suitable manner, such as bya variable cone pulley drive from a line shaft tothe-shaft 43.

. Conveyor 50 is constructed similarly to conveyor 20 and is arrangedtransversely beneath the line of leaching tanks so as to re-- ceive theextracted chips discharged from each of thetanks.

Generally only one or several of the leachin'gtanks will be disrow byconveyor 50 supported on suitable rolls 52 and 53. This conveyordischarges' onto another conveyor 54Which is supported on an inclinationto the'horizontal by rolls .5 5 and 56 and serves to elevate the chipsand discharge them intofthe interior of a rotary cylindrical screenindicated diagrammatically at 58. Screen 581is inclined from the feedingend 59 to the discharge end 60 thereof, so `Vthat the material feedsthrough the.

screen as it is rotated vand discharges therefrom onto another conveyor61. A container 62, built up beneath the screen 58 to receive the finematerial or screenings passing therehoppers 67 through, has a lowerhopper portion G3 feeding into another conveyor 64.

It is found that a better grade of pulp is` produced when the leachedchips are screened to remove the finer sawdust and impurities prior tothe pulping operation. The screenings are quite satisfactory for boilerfuel, so that the conveyor Gamay be arranged to convey them in thedirection. of the'arrow to the boiler fuel supply, or other point ofdischarge. i'

Conveyor 61 moves the screened material in the direction of the arrow tosupply the cooking tanks or digesters. As shown, a plurality ofspherical digesters 65 are mounted in line, each for rotationabouthorizontal trunnions or bearings 66. Positioned above each digester in astorage bin 67 terminating in a converging lower end or hopper 68 conj.trolled by slide valve 69. Each digester is provided with a cover plate70 removably bolted thereto, and so positioned as to be adapted to bebrought into alignment with the valve controlled opening of the feedinghopper 68. Trough 71 of conveyor 61 has a plurality of spaced openings 72 controlled by sliding plates 73, through which the chips moved alongtrough 71 may fall into chutes 74 discharging into the respectivefeeding The chutes are downwardly and laterally inclined so as to beremoved from the path of travel of the lower returning portion of theendless conveyor. The storage bins 67 are adapted to be maintainedfilled,

f or with a sufficient supply of chips, so as to"- provide a completecharge for a digester. In filling, each digester 65 is rotated about thetrunnion 66 until the cover plate 70 is brought into alignment withthe-discharge hopperof the storage bin 67. The cover plate 70 is thenremoved, and the'valve 69 opened to allow the chips to feed into thedigester until a full charge is supplied thereto. The cover plate 70 isthen replaced and the cooking commenced.

' The leached chips are cooked with an incomplete digestion orsemichemical cook which gives a high yield and-'fa product of goodstrength. In the semichemical cook, very. satisfactory results aresecured with a cooking liquor containing a normal sulphite Aand analkali metal salt of a weakly ionized polybasic acid, such as a mixtureof sodium sulphite and sodium carbonate. The cook is generally carriedout in two stages, al-

though it may be carried out in a single stage.

The cooking liquor is introduced from suitable liquor. supply tanks (notshown) through piping passingthrough the hollow trunnions 66 to submergethe chips, temperature is brought up to approximately 125 C. to 150 C.with steam for a length of time to secure desired impregnation of theliquor Within the wood. A treating time of about two hours givessatisfactory results in and the' given in the step of extracting tannicacid from the chips, so that for best results the leachingtreatment andthe subsequent pulp-l ing treatment are coordinated with each other. ltion, the chips are subjected to a controlled leach so as to give auniform residue, or leached chips of 'uniform composition, as a resultof the leaching operation. The degree of leaching treatment is dependentupon the time, temperature, pressure andV volume of leaching liquid orwater used per unit weight of chips. By increasing the time oftreatment, the leaching effect is increased; that is, a greaterproportion of the tannic acid and other readily soluble constituents ofthe Wood are dissolved out of the chips. Similarly by increasing thetemperature or pressure used in the leachingoperation, or by using agreater volume of leaching liquor per unlt weight of chips, the leachingeffect is correspondingly increased. These conditions of leaching,namely, time, temperature, pressure and In accordance with the presentinvenvolume of leaching liquor, are therefore con-py I trolled sosas togive a resulting leached chip which /has a substantially uniformcomposition or residue, this being termed herein for purposes ofdescription a residue controlled leaching operation.

It is also found that the character of the ulped material produced bythe digestion of the leached chips, as well as the character of theultimate sheet formed from such pulp is also dependent upon'the cookingor digesting operation. The degree of cooking treatment is dependentupon the quantity and proportioning of the chemicals used, and the time,temperature and pressure of the cooking operation. The cook iscoordinated with the leaching treatment by suitably controlling andinterconnecting these cooking conditions in accordance with thecharacter of the' Aresidue resulting from the leach. This control andcoordination of the quantity and proportioning of the chemicals, thetime, tcmperature and'pressure of the cook with respect to the inherentcharacteristic effect of each, and also with respect to the pulpingcharacterstics of the residue controlled chips, is

termed herein for purposes of description a form the desired sheet maybe intelligently and readily controlled in commercial operations.

Where chestnutI Wood is used, and the leached chestnut chips resultingtherefrom, are then utilized in the manufacture of paper pulp, it isfound preferableV that the extent of leaching be not increasedmaterially over seventy hours. On the other hand, it is desirable togive a sufiiciently long immersion of the chips during the leachingoperation to obtain mcreased extraction, or a greater yield of tannicacid, without lowering the purity of the extract.- Satisfactory resultshave been secured inactual commercial operations in several plants usingan open tank leach `With a leaching time varying from about thirty toseventy hours, the leaching temperature varying from between 140o F. to212 F. and using approximately 1500 to 1800 gallons of water per longcord of chestnut chips..

It is also found that the proper quantities or relative amounts of thenormal sultite and the carbonate or other alkali metal salt of a weaklyionized polybasic acid such as sodium bicarbonate, sodium borate, andthe like,

.should be utiliz'edin the subsequent semichemical cooking operation.The final characteristics of the ultimate product arenot only affected,but also the handling of the material in the subsequent formation on thepaper machine, if the proper relative amounts are not maintained,lasWell as the proper coordination of this cooking step with the previousleaching operation.

Suilicient sodium carbonate, or other alkali metal salt of a. weaklyionized polybasic acid, should be used to neutralize the organic orpyroligneous acids present in the leached chips and given off during thecook, and to maintain a slight alkalinity of the cooking4 liquor. Theeiicacy of the cooking liquor, or the sodium sulfite as a cooking agent,appears to be enhanced by the maintenance of substantial neutrality ofthe cooking liquor during the cook, a slight alkalinity being preferredto any acidity. It has been found'that the sodium sulfite is the activecooking agent and gives under such conditions the desired Vpulpproducts, and that the function of Ysired neutrality or slightalkalinity of the cooking liquor. The sodium carbonate should thereforebe used in a controlled proportion to tra ity or slight alkalinity, butit should not be used in sufficient proportion to materially affect orreduce the cooking eilicacy of the sodium suliite. Moreover, it is foundthat Where the carbonate is present in quantities materially in excessof that required for neutralization of the acids, then a pulp product ofinferior quality is produced. At the same time, a controlled amount ofsodium sullite, or other alkali metal suliite such as potassium sultite,should be usedin connection with the controlled amount of sodiumcarbonate in order-to give a cooked product of the desiredcharacteristics. -lVith Wood of this character, a certain proportion ofthe acid content, such as tannic acid, is left in the chip residueresulting from the leaching operation; and other acid may be formed byreaction during the cook. By providing a controlled leaching operationsol as to give a uniform residue, the proportions of chemicals ,used inthe cook can thus be maintained uniform and in proper amounts to securethis desired neutralizing and cooking action for a given' chip residue.If it is desired to increase the cooking effect, this may beaccomplished by increasing the proportion of sodium' sulfite used, Whilemaintaining the sodium carbonate constant at that amount Which effectsVthe neutralization of the liberated acids and the maintenance of aslight alkalinity of the cooking liquor.

If it is desired to decrease the cooking effect, this may be broughtabout by decreasing the proportion of sodium sulte, the carbonate beingmaintained constant. By increasing the quantity of carbonate for a givenchip residue, While maintaining the quantity of sulfite constant, it isfound that the net cooking effect is decreased. It is more efficient tovary the proportion of sodium sulfite used Within the above range tovary the cooking effect, as this leaves the carbonate at the properamount for neutralization of the'acidsof a particular chip residue. Bylincreasing the quantity of carbonate materially above this amount, theycooking efficacy ofthe sulite is reduced and a poorer pulp productproduced, this obviously being an ineflicient Way of decreasing thecooking effect.

Where the quantities of chemicals used are altered, such as fordigesters of differ .nt sizes andi-'consequently for different Weightsof chestnut chips leached in the manner described above, lthecarbonateshould be ini creased y.or decreasedin accordance with the acid contentof thc chips to maintain the desired neutrality of the cooking liquor,While the sulfite should be increased or decreased in proportion to thequantity of thewood vive this most elfective condition of neuand thecharacter of the pulp product desired and these chemicals should not bearbitrarily increased or decreased like amounts, if the cookingconditions are to be maintained approximately the same. By themaintenance of coordinated conditions in the residue cont-rolledleaching operation and the reaction controlled cooking operation, and bythe maintenance of the proper relative quantities of chemicals in thecooking operation, a pulp can be uniformly produced in commercialoperation which has high strengtlngood yield and which is susceptible offormation on a forming machine at high speeds. Where this pulp is usedin the manufacture of so-called corrugated board, it has been found inactual operation that the pulp can be passed over a forming machineincluding a conventional corrugating machine at a speed of 250 feet perminute or more without operating diiiculties.

As an example of an operation giving'very satisfactory results, aleaching time in an open tank leach of about thirty-four to fortytwohours at a temperature of about 160 F. to 212 F. using about 1800gallons of Water per long cord of chestnut chips, is mentioned. Thisgives an extract of desirably high purity, for example a purity of atleast as measured on the arbitraryscale used in the extract industry.The leached chip residue resulting from this leaching operation is thencooked in the manner described above with a cooking liquor containingabout 2000 to 2100 pounds of sodium sulfite (calculated as sodiumcarbonate) and about 650 to 700 ounds of sodium carbonate for about 81/2s ort cords of the leached chestnut chips. 'The chemicals may of coursebe used in different relative amounts within a certain operating rangeand in accordance with the pulp product desired. Thus in actualcommercial operations, With a certain character of chestnut chiptreated, and with the leaching operations as s ecified above,satisfactory results have been obtained Where these chemicals arepresent in the cooking liquor in the proportion of substantially 2.5 to3.7 parts b Weight of sodium sulite to one part by weig t of sodiumcarbonate (both chemicals being calculated as sodium carbonate). Thuswith a digester having a capacity of about 8% short cordspf leachedchestnut chips (Weighing on a d ry basis about 19,000 to. 20,000 pounds)satisfactory results in commercial operation have been secured Wheresubstantially 1750 to 2350 pounds of sodiumv sulfite (calculated assodium carbonate) and substantially'650 to 700 pounds of sodiumcarbonate have been used, with cooking conditions -of time, temperatureand pressure as set forth above.

In actual commercial operations, by using a definite substantiallyconstant leaching operation for the different types of chestnut Woodencountered, it is found that a relatively constant tannic acid contentremains in the chip residue for the different types of Wood,

actual tests showing a tannic acid residue varying from about 11/4L to1%%. As a matter of convenience in-such commercial operations, a slightexcess of carbonate, say about iii'ty pounds per digester, isused in thecooking liquor over that required for neutralization of the minimum acidcontent of the chip residue. This excess is suflicient to take care ofthe normal variation of about 1/2% in the tannic acid contentencountered, and to maintain the desired neutrality or slight alkalinityof the cooking liquor; at the same time, this slight excess is notsufficient to materially affect thecooking efficacy of the relativelylarge amount of sulfite or the character of the pulp product obtained.

Altering the leaching operation has the effect of removing variablequantities of materials in the leaching step, Which throws disturbancesin the reaction stage. For a certain set of conditions in the leachingstage, al uniform residue may be secured with a particular Wood, andthis residue may then be tested/to ascertain its retained acid and non!The subsequent cooking cell'iose content. may then be properlycoordinated therewith, inasmuch as when the residue content of the chipis known, a proper cooking operation for that residue content will givea pulp of the desired and uniform quality, and the conditions of cookingfor a particular residue content may be readily ascertained byexperiment or experience. Consequently, it is only necessary in the.commercial operations to choose the properly coordinated cookingoperation for a certain ascertained residue content, so as to obtain thedesired ultimate product. And by controlling the leaching operation soas to maintain this residue content uniform at an ascertained value, theentire operation may be carried out in practice with relativelyunskilled labor and without extended chemical analysis for eachparticular operation, and a uniform tannic acid extract of desiredpurity and a uniform pulp product of controlled quality obtained. l

As an example of altered conditions, a

leaching time of about sixty to seventy hours at a temperature of about160 F. to 212 F. and using about 1800 gallons of Water per long cord ofchestnut chips, gives satisfactory results with the employment of asubsequent cook in a liquor containing about 1800 to 1900 pounds ofsodium sulfitef(calculated as sodium carbonate) and about' 625 to 675pounds of sodium carbonate per 81/2 short cords of leached chestnutchips. given above refer to open tank leaches. Where autoclave leachesare used, satisfactory results have been obtained with a' temperaturerange of about 160 F. to 250 F., using about 1000 to l1200 gallons ofWater per The figures Y board, the Ldigester is preferably not blown butis merely dumped so that the softene. material is not shredded orpulped'at this stage butis maintained in chip form, Whereby it is easilyhandled at high density, i. e. low moisture content. The mass ofsoftened chips discharged into each dump tank 75 is then Washed toremove residual liquor. This may be accomplished by the introduction ofsprays of Washing liquid through valve controlled pipes 76, the liquordraining through a. perforated partition or latticework 77 Within thebottom of the dump tank, and escaping by a valve controlled outlet pipe78 communicating with a. drain 79. i Each dump tank 7 5' is providedwith mean for feeding the softened and drained chips at a controlledrate to subsequent treating apparatus, such as a rod millor othermechanical disintegrating apparatus for reducing thesoftened chips topulp. As illustrated, each dump tank 75 is provided with a leach casterconstruction including a central vertical shaft 80 carrying a slidingarm 81, the shaft 80 being driven by intermeshing gears 82 and 83 from adriven shaft 84 adapted to be connected to a suitable source of power. Avalve controlled opening 86l is provided inthe grid 77 in alignment witha valve controlled discharge pipe 87, so that drained chips may bedischarged at a controlled rate therethrough onto a traveling conveyor88 common to all the dump tanks and Which carries them in the directionof the arrow to the subsequent treating apparatus. The digesters arepreferably cooked in rotation, so that one or several are cooking Whileanother is being dumped. Thus the softened chips in one dump tank, afterWashing and draining, may be fed slowly and at a controlled rate fromthe dump tank by the leach caster during the time thatl another batch ofchips is being cooked in its respective digester, and still anotherbatch of chips in another dump tank is being Washed and drained.

While the method herein described, and the form of apparatus forcarrying this method into effect, constitute preferred embodiments ofthe invention, it is to be understood that the invention is not limitedcise method and form of apparatus, and that changes may be made ineither Without departing from the scope of the invention which isdefined in the appended claims.

What is claimed is:

1. In the pulping of acid containing deciduous Woods, the method whichcomprises leaching the woods to extract a substantial creasing to thispreproportion of the soluble contents therefrom While leaving aproportion of the more dithcultly soluble acid content in the Woods tomaintain the purity of the extract, cooking the previously leached Woodsin a liquor containing a normal suliite and an' alkaline material, thenormal sulte being controlled as to amount to give a controlled cookingaction such as to soften the Woods without pulping so asto provide forsubsequent disintegration to pulp, and the quantity of alkaline materialbeing controlled in accordance with the -residual acid content of thewoods to neutralize the resid'ual acid in the leached Woods and suchacid asmay be generated during thel cooking action /and insuicient to`materially affect the cooking action of the normal sulfite ordeleteriously affect the pulp product.

2. In the pulping of chestnut chips, the method which comprises leachingthe chips to extract a substantial proportion of the soluble contentstherefrom While leaving a proportion of the more diiiculty soluble acidcontent in the chips to maintain the purity of the extract, cooking thepreviously leached chips with a cookingliquor containing an alkali metalsulite and an alkali metal carbonate in the proportions of substantially2.5 to 3.7 parts by Weight of the alkali metal sultite (calculated assodium carbonate) to one part by Weight of the alkali metal carbonate(calculated as sodium carbonate), and inor decreasing the quantity ofthe alkali metal sulite Within the proportions specified Whilemaintaining the quantity of the alkali metal carbonate substantiallyconstant to respectively increase or decreasethe cooking effect.

3. In the extraction of tannic acid from acid containing deciduous Woodchips and the pulping of extracted Wood chips, `the method whichcomprises leaching the deciduous Wood chips with water to extract asubstantial proportion ofthe soluble contents therefrom While leavmg auniformly controlled acid residue in the chips so as to maintain thepurityV of the extract, then subjecting the leached chips to acontrolled pulping treatment including cooking in a liquor containinganormal alkali metal suliite and the alkali metal salt of a weaklyionized polybasic acid, the pulping treatment being coordinated with theprevious leaching treatment by varyingv the quantity of thealkali lyionized polybasic acid used yint e cooking liquor in accordance with theacid'residue of the leached deciduous Wood chips to maintain substantialneutrality or a slight alkalinity of the cooking liquor during thecooking operation, and varying the quantity of normal alkali metalsulite used in accordance with metal salt-of a Weakthe quantity of Woodand the pulp product desired.

4. In the extraction of tannic acid from chestnut chips and the pulpingof extractedchips, the method which comprises leaching theacid'containing chestnut chips in Water at substantially atmosphericpressure for a period of time not exceeding 70 hours to extract asubstantial proportion of the soluble contents therefrom While leaving'a proportion of the moredifcultly soluble acid content in the chips tomaintain the purity of the extract, and then-subjecting the leachedchips to a pulping treatment including cooking 'with a cooking liquorcontaining substantially 2.5 to 3.7 parts by weight of sodium sulfite(calculated as sodium carbonate) and one part 4by Weight of sodiumcarbonate, the cooking treatment being controlled to coordinate the samewith the previous leaching treatment by controlling the Vquantity ofsodiumI carbonate Within the proportions specified in accordance Withthe residual acid y content of the leached chips, and by controlling theVquantity of sodium sulite Within the proportions specified inaccordance With the Aquantity of Wood and the degree of softeningdesired in the cooking operation.

5. Apparatus of the,character described, comprising in combination, aleaching tank for extracting tannic acid from Wood chips, draining meansfor said leaching tank, means for discharging leached chips at acontrolled rate from said tank, a storage bin, conveying means fortransporting said chips as discharged from said leaching tank to saidstorage bin, a digester, and means for introducing the chips from saidstorage bin into said digester. f i

6. Apparatus of the character described,

comprising in combination, a plurality of leaching tanks arranged inline, a conveyor extending transversely of said tanks for receivingmaterial discharged from each of said plurality of leaching tanks, aplurality of digesters, storage bins for 'said digesters positioned inlinev and in feeding relation with said digesters, a conveyor extendingtransversely of said storage bins for feeding material into each of saidstorage bins, and means for transferring material from said firstmentioned conveyor to said last mentioned conveyor.

7 Apparatus of the character described, comprising in combination, aplurality of digesters, a plurality of dump tanks positioned in line andarranged to receive material discharged from said digesters, drainingmeans for each of said dump tanks, means for discharging drainedmaterial of low moisturecontent at a controlled rate from. each of saiddump tanks, and a common conveyor for receiving material as dischargedfrom each of said Adump tanks and for transporting the material to asubsequent treating apparatus.

8. Apparatus of the character described comprising in combination, aplurality o leaching tanks arranged in line, a conveyor digesters forreceiving material discharged therefrom, means for discharging materialfrom each of said dump tanks, and a conveyor common to all said dumptanks for receiving material discharged therefrom and for conveying itto subsequent treating apparatus.

In testimony whereof I hereto aix my signature.

l CHARLES' S. HAMM;

